Process of making friction facings



Patented -Apr. 15, 1930 UNITED STATES PATENT OFFICE EDWIN E. WAITE, OFFRAMING'HAM, MASSACHUSETTS, ASSIGNOR T MULTIBESTOS COMPANY, OFWALPOLE,-MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS PROCESS OF MAKIN'G FRICTION FAOINGS No Drawing.

This invention relates to the manufacture of brake linings, clutchfacings and similar friction facings.

Facings of this character usually consist of 1' this manner even'whenthe blank is subjected to preliminary heating and vacuum treatinents andthe best impregnating methods are followed. The difficulty appears to bethat the asbestos fibre is an exceptionally good filter and it strainsout the more viscous constituents of the impregnating liquids.

This condition has long been recognized and various expedients have beenadoptedto produce a more uniform and thorough im-.

pregnation. Among these expedients may be mentioned particularly thoseof making the facing blanks more porous so that they Will to absorb theimpregnating liquid more readily,

and subjecting the facings to double impregnating'and baking processes.

p The presentinvention is especially concerned with the problempresented by these conditions in the felted or unwoven type of frictionfacings. It aims to devise a thoroughly practical solution for thisproblem, and in addition to provide a process for incorporating bindersin solid form in friction facings of this type.

It' is a further object of this invention to improve both thecomposition of friction fac ings and the methods of making them with aview to eliminating the squealing or squeaking which is very likely tooccur when a brake or clutch is being applied or is takinghold,

and which is extremely annoying.

The nature of the inventipn'will be readily understood from thefollowing description of a preferred method of procedure, and theApplication filed January 16, 1929. Serial No. 333,031.

novel features will be particularly pointed out in the appended claims.

According to a typical process embodying or the common dryers used withdrying oils are satisfactor for this purpose. After a brief period 0further beating or agitating the drying oil is added to the mass in thebeater. Preferably an emulsion of a drying oil such as linseed oil,china wood oil, or the like is used, the emulsion being made by any ofthe well known methods. Assuming that a thousand pounds of asbestosfibre is originally introduced into the beater, about four hundredpounds of a 60% drying oil emulsion is suitableand approximatelytwentyfive pounds of red lead of similar dryer.

For a time after the emulsion is added the roll of the beater may beleft in an elevated position where it acts simply as an agitator.

and later lowered to its usual position. The asbestos fibre tends tosettle to the bottom of the beater after the introduction of the oilemulsion and the mass therefore should be stirred with paddles for aconsiderable length of time, say half an hour, in order to lift thefibre and agitate the entire body of stock.

Gradually the fibre takes up the oil and rises to the surface of the.water.

If a pulverized binder or filler is to be added to the fibre it can beintroduced at practically any stage of the beating operation. 1 considerit preferable, although not at all necessary, to'introduce suchpulverized solids after the fibre has become thoroughly wetted or coatedwith the drying oil or other liquid binder used. If gilsonite or otherhigh melting oint asphalts are to be incorporated in the acingasbinders, they maybe added at this stage of the process. For a batch ofasbestos fibre of the weight above mentioned I prefer to add about onehundred and thirtyfive pounds of pulverized gilsonite to the mass in thebeater and to continue the agita tion or beatingv so that the pulverizedmaterial will adhere to the fibre. Such adhesion appears to befacilitated very materially by the fact that the fibre is already moreor less saturated with the oil. The greater part of the red lead orother oxidizing agent used has previously become attached to the fibre.

In order to fix these pulverized solids more firmly to the fibre, asufiicient quantity of a solution of alum or equivalent material isadded to the beater mixture at this point to give the entire mass anacid reaction. For the batch above mentioned about one hundred pounds ofalum is dissolved in a barrel of water and added to the mixture, thebeating being continued to mix the solutionthoroughly with the othermaterials in the beater.

The fibre so prepared may now be used in making a friction facing blankaccording to any suitable process. I prefer to make'this fibre into asheet or board and then to cut the facing blanks out of the sheetmaterial so produced. For this purpose the fibre is drawn from theheater to a stufi' chest and is then run to a board machine or, papermaking machine of the cylinder type where a laminated board is built upin the usual manner. The addition of the alum to the beater bathprevents the separation of the gilsonite, red

' lead, or other pulverized materials from the fibre which otherwisewould occur. No substantial separation actually takes place, however,when the alum is used and the alum also seems to harden the fibre.

It will be clear that the board prepared in this manner has drying oildistributed substantially. uniformly through it, and if gilsonite orsome other pulverized binder or filler is used, such material also isdistributed very uniformly throughout the entire structure of the board.The production of a board in this manner, however, permits a veryaccurate control of the entire manufacturing process, and results in afar more uniform and homogeneous product than can be produced by anyother method of which I have been able to learn.

The further operations performed on the board so produced will dependvery largely upon the nature of the final product to be made. In makinbrake linings and clutch facings the board usually is pressed underheavy pressure to squeeze out the surplus water and then preferably isallowed to rest or season for at'least two or three weeks. Ex-

actly what occurs in this seasoning process is is calendered, thefriction facings are died out to shape, and in the case of brake liningsor shoes the blanks produced by the cutting or dieing out operatlon arenext bent to the very thorough oxidation of the drying oil takes placeat this time. Additional binder may be added to the blanks at this stageof the process, if desired, by soaking them in a liquid binder. Forexample, they may be immersed in a solution of, say, sixty parts ofchina Wood or linseed oil dissolved in forty parts of naphtha. If theyare placed in this ath immediately after being dried and while they arestill warm, they will absorb quite a high percentage of the bath in halfor three-quarters of an hour. WVhen liquid binder is thus added to therings by saturation they are next allowed to drain and are thensubjected to an additional drying operation at 150 F;, for example, forabout twelve hours. Next the facings are pressed in molds under heavyhydraulic pressure to bring them down to approximately the desiredthickness and they are then baked for about two hours at a considerablyhigher temperature than any to which they formerly have been subjected,a temperature of 375 being suitable. This baking operation is performedeven when the saturating step is omitted, but for most products thisstep is desirable.

The facings now may be finished in any desired way, usually by drillingand counterboring them to receive the rivets by which they are to befastened to the brake bands or metal clutch rings, and by surfacegrinding to size them accurately. In some cases these facings areredipped and baked a second time in or er to give them an exceptionallyhard shell, but this is rarely advisable.

The process above described produces fric tion facings which areexceptionally homogeneous in structure, due chiefly to the fact that thebinder is distributed very uniformly throughout the entire body of thefacing. This is accomplished by wetting the fibre thoroughly withoxidizing oil while it is in the beater and by attachmg the pulverizedbinder, if one is used, to the fibre at this time. As above stated, thepulverized binder usually consists of a high melting point asphalt, andwhile it is attached to the fibre in a solid condition, this binderlater is melted in the drying and baking of the facings and soaks intothe fibre at th1s time. A far more uniform impregnation of the facingboth with drying oils and also with gilsonite or other solid binders,such as resins, is obtained by this process than can be produced by anyof the prior methods of which I am aware- Furthermore, these materialsareused economically which is important from a manufacturing standpoint,especially when ex pengive granular or pulverized binders are use Inmaking certain friction facings', particularly brake linings, a part orall of the gilsonite or other high melting point asphalt is omitted, andin place of it a corresponding quantity of graphite is added to thebeater, preferably at the point in the process at which the gilsonitewas added. The pulverized graphite of commerce, such as Dicksons orAchesons, may be used. This material will adhere readily to the fibre,particularly after it has become more or less saturated with oil in thebeater, and it is firmly attached to the fibre when the bath is madeslightly acid. The remaining steps of the process are carried outsubstantially as described above.

This addition of graphite and its distribution uniformly throughout thefacing is particularly desirable in making brake linings where thegraphite has the effect of modifying the coefficient of friction, and isespecially valuable in preventing the squealing of the brakes which isso annoying. So far as I am aware, graphite has not been successfullyintroduced heretofore in friction facings of this type. 7

While a typical method of procedure has been above described, it will beunderstood that this disclosure has been made rather by Way ofillustration than limitation, and that considerable variation may bemade in the procedure without departingfrom the spirit or scope of theinvention. For example, the body forming material has been referred toas asbestos fibre, but it may be desirable for special purposes to addto the asbestos other materials, such as paper stock, although apredominating percentage of asbestos fibre is always used.

Having thus described'my invention, what I desire to claim as new is:

1'. A friction facing comprising a shaped body of unwoven feltedasbestos fibre and a binder distributed substantially. uniformlythroughout said body and cured by heat, said facing also having apulverized lubricating filler distributed substantially uniformlythroughout the body portion thereof.

2. A friction facing comprising a shaped body of unwoven felted asbestosfibre united by a heat resisting binder distributed substantiallyuniformly throughout the facing, said facing also including asubstantial pera friction facing blank from said fi asbestos fibre in aliquid medium until it isv thoroughly opened. Wetting said fibrethoroughly with a binder while the fibre is suspended in said medium,making a friction facing blank from said fibre, and subsequently curingsaid binder with heat. 3

5. That improvement in processes of making friction facings whichconsists in beating asbestos fibre in a liquid medium until it isthoroughly opened, wetting said fibre thoroughly with a drying oil whilethe fibre is suspended in said medium, making a friction facing blankfrom the fibre so prepared, and subsequently oxidizing said oil.

6. That improvement in processes of making friction facings whichconsists in heating asbestos "fibre in a liquid medium unt1l it isthoroughly opened, wetting said fibre thoroughly with a drying oil whilethe fibre s suspended in said medium, making a lam1- nated board fromthe fibre so prepared, cutting friction facing blanks from said board,and subsequently oxidizing said drying 011.

7. That improvement in processes of making friction facings, whichconsists 1n beating asbestos fibre in a liquid medium until the fibre isthoroughly opened, causing a pulverized binder to adhere to said fibrewhlle the fibre is suspended in said liquid, making a friction facingblank from said fibre, and

subsequently heating said blank sufliciently to melt said binder.

8. That improvement in processes of making friction facings, whichconsists in heating asbestos fibre in a liquid med um untll the fibre isthoroughly opened, causlng a pulverized binder to adhere to said fibrewhile the fibre is suspended in said liquid making bre, adding aliquidbinder to said facing by saturation, and later heating the blankfso treated sufficiently to melt said pulverized binder and to cure saidliquid binder. tr

9. That improvement in processes of mak-' ing friction facings, whichconsists in beating asbestos fibre in a liquid med um until the fibre isthoroughly opened, causing a ulverized binder to adhere to said fibre wile the fibre is suspended in said liquid, making a friction facingblank from said fibre, at some stage in the process wettingsubstantially all of the fibre of said blank with a drying oil, andsubsequently oxidizing said oil and melting said pulverized binder.

10. That improvement in processes of making friction facings whichconsists in beating asbestos fibre in a liquid medium until 1t isthoroughly opened, causing powdered graphite to attach itself to thefibre while the fibre is sus ended in said medium, making a frictionacing blank from the fibre so prepared, at some stage in the processwettin substantially all of the asbestos fibre of sai facing with aliquid binder, and subsequently curing said binder with heat. 11. Thatimprovement in processes of mak ing friction facings which consists inbeating asbestos fibre in a liquid medium until it is thoroughly opened,causin said fibre to absorb a drying oil while the fi re is suspended insaid medium, attaching powdered graphite to said suspended fibre, makinga friction facing blank from the fibre so prepared, and subsequentlyoxidizing said oil.

12. That improvement in processes of makin friction facings whichconsists in beating as estos fibre in a liquid medium until it isthoroughly opened, causing said fibre to absorb a drying oil while thefibre is suspended in said medium, attaching powdered graphite to saidsuspended fibre, making a laminated board from the fibre so prepared,cutting friction facing blanks from said-board, and subsequentlyoxidizing said drying oil.

13. That improvement in processes of making friction facings whichconsists in beating asbestos fibre in a liquid medium until it isthoroughly opened, causing said fibre to absorb a drying oil while thefibre is susended in said medium, attaching a pulverized solid materialto said suspended fibre,

making a laminated board from the fibre so prepared, cutting frictionfacing blanks out of said board, drying the blanks, immersing the dryblanks in a liquid binder, and subsequently baking the blanks so treatedat a high temperature.

14. That improvement in processes of making friction facings whichconsists in beating as estos fibre in a liquid mdiumimtil it isthoroughly opened, causing said fibre to take up a drying oil while thefibre is suspended in said medium, attaching a pulverized binder to saidsuspended fibre, forming a laminated board from the fibre so' prepared,cutting friction facing blanks out of said board, and

subsequently heating said blank sufliciently to melt said powderedbinder and to oxidize said drying oil. v EDWIN E. VVAITE,

